The human nervous system is used to send and receive signals. The pathway taken by the nerve signals conveys sensory information such as pain, heat, cold and touch and command signals which cause movement (e.g. muscle contractions).
Often extraneous, undesired, or abnormal signals are generated (or are transmitted) along nervous system pathways. Examples include, but are not limited to, the pinching of a minor nerve in the back, which causes extreme back pain. Similarly, the compression or other activation of certain nerves may cause referred pain. Certain diseases also may compromise the lining of nerves such that signals are spontaneously generated, which can cause a variety of maladies, from seizures to pain or (in extreme conditions) even death. Abnormal signal activations can cause many other problems including (but not limited to) twitching, tics, seizures, distortions, cramps, disabilities (in addition to pain), other undesirable conditions, or other painful, abnormal, undesirable, socially or physically detrimental afflictions.
In other situations, the normal conduction of nerve signals can cause undesirable effects. For example in cosmetic applications the activation of the corrugator supercilli muscle causes frown lines which may result in permanent distortion of the brow (or forehead); giving the appearance of premature aging. By interruption of the corrugator supercilli activation nerves, this phenomenon may be terminated. Direct surgical interruption of nerves is however a difficult procedure.
Traditional electrosurgical procedures use either a unipolar or bipolar device connected to that energy source. A unipolar electrode system includes a small surface area electrode, and a return electrode. The return electrode is generally larger in size, and is either resistively or capacitively coupled to the body. Since the same amount of current must flow through each electrode to complete the circuit; the heat generated in the return electrode is dissipated over a larger surface area, and whenever possible, the return electrode is located in areas of high blood flow (such as the biceps, buttocks or other muscular or highly vascularized area) so that heat generated is rapidly carried away, thus preventing a heat rise and consequent burns of the tissue. One advantage of a unipolar system is the ability to place the unipolar probe exactly where it is needed and optimally focus electrosurgical energy where desired. One disadvantage of a unipolar system is that the return electrode must be properly placed and in contact throughout the procedure. A resistive return electrode would typically be coated with a conductive paste or jelly. If the contact with the patient is reduced or if the jelly dries out, a high-current density area may result, increasing the probability for burns at the contact point.
Typical bipolar electrode systems are generally based upon a dual surface device (such as forceps, tweezers, pliers and other grasping type instruments) where the two separate surfaces can be brought together mechanically under force. Each opposing surface is connected to one of the two source connections of the electrosurgical generator. Subsequently, the desired object is held and compressed between the two surfaces. When the electrosurgical energy is applied, it is concentrated (and focused) so that tissue can be cut, desiccated, burned, killed, stunned, closed, destroyed or sealed between the grasping surfaces. Assuming the instrument has been designed and used properly, the resulting current flow will be constrained within the target tissue between the two surfaces. One disadvantage of a conventional bipolar system is that the target tissue must be properly located and isolated between these surfaces. Also, to reduce extraneous current flow the electrodes can not make contact with other tissue, which often requires visual guidance (such as direct visualization, use of a scope, ultrasound or other direct visualization methods) so that the target tissue is properly contained within the bipolar electrodes themselves, prior to application of electrical energy.
In recent years, considerable efforts have been made to refine sources of RF or electrical energy, as well as devices for applying electrical energy to specific targeted tissue. Various applications such as tachyarrhythmia ablation have been developed, whereby accessory pathways within the heart conduct electrical energy in an abnormal pattern. This abnormal signal flow results in excessive and potentially lethal cardiac arrhythmias. RF ablation delivers electrical energy in either a bipolar or unipolar configuration utilizing a long catheter, similar to an electrophysiology (EP) catheter. An EP catheter consisting of a long system of wires and supporting structures normally introduced via an artery or vein which leads into the heart is manipulated using various guidance techniques, such as measurement of electrical activity, ultrasonic guidance, and/or X-ray visualization, into the target area. Electrical energy is then applied and the target tissue is destroyed.
A wide variety of technology in the development of related systems, devices and EP products has already been disclosed. For example, U.S. Pat. No. 5,397,339, issued Mar. 14, 1995, describes a multipolar electrode catheter, which can be used to stimulate, ablate, obtain intercardiac signals, and can expand and enlarge itself inside the heart. Other applications include the ability to destroy plaque formations in the interior of lumens within the body; using RF energy applied near, or at the tip of, catheters such as described in U.S. Pat. No. 5,454,809 and U.S. Pat. No. 5,749,914. In these applications a more advanced catheter which is similar to the EP catheters described above contains an array of electrodes that are able to selectively apply energy in a specific direction. Such devices allow ablation and removal of asymmetric deposits or obstructions within lumens in the body. U.S. Pat. No. 5,098,431 discloses another catheter based system for removing obstructions from within blood vessels. Parins, in U.S. Pat. No. 5,078,717 discloses yet another catheter to selectively remove stenotic lesions from the interior walls of blood vessels. Auth in U.S. Pat. No. 5,364,393 describes a modification of the above technologies whereby a small guide wire which goes through an angioplasty device and is typically 110 cm or longer has an electrically energized tip, which creates a path to follow and thus guides itself through the obstructions.
In applications of a similar nature, catheters which carry larger energy bursts, for example from a defibrillator into chambers of the heart have been disclosed. These catheters are used to destroy both tissues and structures as described in Cunningham (U.S. Pat. No. 4,896,671).
Traditional treatments for the elimination of glabellar furrowing have included surgical forehead lifts, resection of corrugator supercilli muscle, as described by Guyuron, Michelow and Thomas in Corrugator Supercilli Muscle Resection Through BlepharoplastyIncision., Plastic Reconstructive Surgery 95 691-696 (1995). Also, surgical division of the corrugator supercilli motor nerves is used and was described by Ellis and Bakala in Anatomy of the Motor Innervation of the Corrugator Supercilli Muscle: Clinical Significance and Development of a New Surgical Technique for Frowning., J Otolaryngology 27; 222-227 (1998). These techniques described are highly invasive and sometimes temporary as nerves regenerate over time and repeat or alternative procedures are required.
More recently, a less invasive procedure to treat glabellar furrowing involves injection of botulinum toxin (Botox) directly into the muscle. This produces a flaccid paralysis and is best described in The New England Journal of Medicine, 324:1186-1194 (1991). While minimally invasive, this technique is predictably transient; so, it must be re-done every few months.
Specific efforts to use RF energy via a two needle bipolar system has been described by Hernandez-Zendejas and Guerrero-Santos in: Percutaneous Selective Radio-Frequency Neuroablation in Plastic Surgery, Aesthetic Plastic Surgery, 18:41 pp 41-48 (1994) The authors described a bipolar system using two parallel needle type electrodes. Utley and Goode described a similar system in Radio-frequency Ablation of the Nerve to the Corrugator Muscle for Elimination of Glabellar Furrowing, Archives of Facial Plastic Surgery, January-March, 99, VI P 46-48, and U.S. Pat. No. 6,139,545. These systems were apparently unable to produce permanent results possibly because of limitations inherent in a two needle bipolar configuration. Thus, as is the case with Botox, the parallel needle electrode systems would typically require periodic repeat procedures.
There are many ways of properly locating an active electrode near the target tissue and determining if it is in close proximity to the nerve. Traditional methods in the cardiac ablation field have included stimulation by using either unipolar and bipolar energy by means of a test pacemaker pulse prior to the implantation of a pacemaker or other stimulation device. A method of threshold analysis called the ‘strength duration curve’ has been used for many years. This curve consists of a vertical axis (or Y-axis) typically voltage, current, charge or other measure of amplitude, and has a horizontal axis (or X-axis) of pulse duration (typically in milliseconds). Such a curve is a rapidly declining line, which decreases exponentially as the pulse width is increased.
Various stimulation devices have been made and patented. One process of stimulation and ablation using a two-needle system is disclosed in U.S. Pat. No. 6,139,545. The stimulation may also be implemented negatively, where tissue not responsive to stimulation is ablated as is described in U.S. Pat. No. 5,782,826 (issued Jul. 21, 1998).